Human Health and Ecological Risk Assessment for the Use 

of Wildlife Damage Management Methods by APHIS-Wildlife 

Services

Chapter XXXI

USE OF BRODIFACOUM IN WILDLIFE 

DAMAGE MANAGEMENT

Draft 

March 2024
2

Table of Contents

1 INTRODUCTION ................................................................................................................ 5

1.1 Use Pattern of Brodifacoum......................................................................................... 5

2 PROBLEM FORMULATION...............................................................................................10

2.1 Physical and Chemical Properties...............................................................................11

2.2 Environmental Fate.....................................................................................................11

2.3 Hazard Identification ...................................................................................................12

2.3.1 Mechanism of Action and Metabolism..................................................................13

2.3.2 Toxicity ................................................................................................................14

2.3.3 Sub-chronic/Chronic Toxicity ...............................................................................15

2.3.4 Developmental and Reproductive Effects ............................................................15

2.3.5 Neurotoxicity and Immunotoxicity Effects.............................................................15

2.3.6 Carcinogenicity and Mutagenicity.........................................................................16

2.3.7 Endocrine System Effects....................................................................................16

2.3.8 Toxicity of Other Ingredients ................................................................................16

3 DOSE-RESPONSE ASSESSMENT...................................................................................17

3.1 Human Health Dose-Response Assessment ..............................................................17

3.2 Ecological Effects Analysis .........................................................................................17

3.2.1 Aquatic Effects Analysis.......................................................................................17

3.2.2 Terrestrial Effects Analysis...................................................................................18

4 EXPOSURE ASSESSMENT..............................................................................................20

4.1 Human Health Exposure Assessment.........................................................................20

4.1.1 Identification of Potentially Exposed Human Populations and Complete Exposure 

Pathways ...........................................................................................................................20

4.1.2 Occupational Exposure Evaluation ......................................................................22

4.2 Ecological Exposure Assessment ...............................................................................23

4.2.1 Aquatic Exposure Assessment ............................................................................23

4.2.2 Terrestrial Exposure Assessment ........................................................................24

5 RISK CHARACTERIZATION .............................................................................................26

5.1 Human Health.............................................................................................................26

5.2 Ecological Risks..........................................................................................................27

5.2.1 Aquatic.................................................................................................................27

5.2.2 Terrestrial ............................................................................................................28

6 UNCERTAINTIES AND CUMULATIVE IMPACTS .............................................................32

7 PREPARERS: WRITERS, EDITORS, AND REVIEWERS .................................................33

7.1 APHIS WS Methods Risk Assessment Committee......................................................33

7.2 Internal Reviewers ......................................................................................................34
3

8 LITERATURE CITED.........................................................................................................36
4

EXECUTIVE SUMMARY

Brodifacoum is a toxicant registered to control rodents under a variety of agricultural and 

nonagricultural uses. The United States Department of Agriculture (USDA), Animal and Plant 

Health Inspection Service (APHIS), Wildlife Services (WS) uses brodifacoum for conservation 

purposes to eradicate invasive rodents on islands and to control rodents around non-residential 

manmade structures. APHIS is the registrant for two brodifacoum end use bait products

(Brodifacoum-25D Conservation and Brodifacoum-25W Conservation). Both bait products are

restricted use pesticides for sale and use by employees of federal agencies responsible for wildlife 

management or persons working under their authority. Additional brodifacoum products may be 

registered and used by WS and cooperators under supplemental labels for specific island 

projects. WS also uses Talon® Weatherblok® XT for rodent control near manmade structures in 

projects not associated with island conservation.

USDA APHIS evaluated the potential human health and ecological risks from the proposed use 

of brodifacoum to control island rodent damage; the evaluation also includes WS minor use of 

brodifacoum in non-island projects. Brodifacoum is a second-generation anticoagulant. 

Brodifacoum is acutely toxic through oral, dermal, and inhalation exposure routes (Toxicity 

Category I) and a mild eye irritant (Toxicity Category III). Dermal irritation was not tested because 

of its high dermal toxicity, but brodifacoum did not cause dermal sensitization. Although the 

human hazard potential for the technical active ingredient is high, risks from WS use of the 

brodifacoum bait formulations will be low because of the low toxicity of the baits (0.0025–0.005% 

brodifacoum) and the anticipated minimal human exposure. Exposure is greatest for workers who 

handle and apply the bait; however, required use of personal protective equipment by applicators 

results in low potential for exposure and risk when factoring in available health effects. The 

potential exposure and risk to the public is low due to the use pattern and label restrictions, as 

well as the lack of dietary exposure through food, feed, or drinking water. 

Ecological risks to aquatic nontarget organisms are low based on the use pattern, available 

toxicity data, and labeled mitigation measures designed to reduce exposure to aquatic habitats. 

Risks to terrestrial invertebrates and plants are also low based on available effects data and the 

method of application. Risk is most significant for sensitive terrestrial nontarget vertebrates, 

particularly birds, but these risks can be reduced with label requirements and other mitigation 

measures designed to reduce exposure.
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1 INTRODUCTION

Brodifacoum is a rodenticide used by the U.S. Department of Agriculture (USDA), Animal and 

Plant Health Inspection Service (APHIS), Wildlife Services (WS) to eradicate invasive rodents for 

island conservation purposes, as well as control rodents near non-residential manmade 

structures. This human health risk assessment (HHRA) and ecological risk assessment (ERA) 

provides a qualitative evaluation of potential risks and hazards to human health and the 

environment, including nontarget fish and wildlife. The methods used for the human health risk 

assessment to assess potential human health effects follow standard regulatory guidance and 

methodologies and generally conforms to methods used by the U.S. Environmental Protection 

Agency (USEPA) (National Research Council 1983, USEPA 2016b). The methods used for the 

ecological risk assessment to assess potential ecological risk to nontarget fish and wildlife

generally follow USEPA methodologies (USEPA 2016b).

This risk assessment uses a standard approach of first identifying the hazard during problem 

formulation. Next, the toxicity of the hazard is evaluated in the dose-response assessment, 

followed by the determination of potential exposure populations and pathways. Lastly, the toxicity 

and exposure assessment information are integrated into the risk characterization (determining 

whether there is adverse human health and ecological risk). This risk assessment also includes 

a discussion of the uncertainties associated with the risk assessment and cumulative impacts.

1.1 Use Pattern of Brodifacoum

A variety of brodifacoum baits are currently registered with the USEPA for the control of 

commensal rodents in structures and areas near human habitats (USEPA 2016c). Brodifacoum 

is also one of the anticoagulant rodenticides shown to be effective for conservation efforts where 

invasive rodents are present on islands (Witmer et al. 2007). APHIS is the registrant of two 

brodifacoum bait formulations that contain 0.0025% weight per weight (w/w) brodifacoum.

Brodifacoum-25D Conservation (USEPA Reg. No. 56228-37) is formulated for “dry"

environments. Brodifacoum-25D Conservation is susceptible to degradation in wetter

environments, so Brodifacoum-25W Conservation (USEPA Reg. No 56228-36) was developed

by Bell Laboratories, Inc. (Madison, Wisconsin) for use in “wet” environments. Both formulations 

are pelleted baits that can be applied using hand spot baiting methods and ground and aerial 

broadcast applications under their Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA)

Section 3 labels (USEPA 2019a;b).

To date, APHIS has worked with Federal partners such as the U.S. Fish and Wildlife Service

(USFWS) and U.S. Air Force (USAF), non-governmental organizations such as Island 

Conservation (IC), and the bait manufacturer Bell Laboratories to conduct or facilitate applications 

of these brodifacoum products to islands for rodent eradication projects. APHIS has also 

registered island-specific supplemental labels with USEPA for these products that allow higher 

broadcast application rates and additional use sites and hand spot baiting methods for those 

rodent eradication projects. WS has also worked with Federal partners to conduct monitoring 

activities following application of brodifacoum products to islands to assess distribution and 

density of bait, bait availability for targets, and to document non-target effects through carcass 

searches.

Currently, APHIS has a Brodifacoum-25W Conservation supplemental label registered for

eradication of Polynesian (Pacific) rats (Rattus exulans) on Wake Atoll by the WS, USAF, and IC, 

which is scheduled for spring 2024 (Table 1). Another invasive rodent species that was recently 

accidentally introduced to Wake Atoll, white-throated woodrats (Neotoma albigula), will be 

removed from Wake Atoll at the same time. This will be the second invasive rodent eradication 
6

project for Wake Atoll. The first eradication project in 2012 using Brodifacoum-25W Conservation 

under a supplemental label successfully eradicated the Asian house rat (R. tanezumi) but not the 

Polynesian rat (R. exulans) from Wake Atoll.

APHIS also has a current Brodifacoum-25D Conservation supplemental label registered for 

eradication of house mice (Mus musculus) on Midway Atoll National Wildlife Refuge’s Sand Island

by USFWS and IC (Table 1). However, bait applications for the Midway Atoll house mouse 

eradication project were discontinued in summer 2023 after the primary broadcast applications

and follow up baiting attempts to kill surviving mice were unsuccessful (USFWS 2024).

APHIS has also submitted a supplemental label application to USEPA in spring 2024 for 

Brodifacoum-25D Conservation to allow USFWS, IC, and WS to conduct an eradication project 

to remove the black rat (R. rattus) from Savana Island near St. Thomas (U.S. Virgin Islands); this 

supplemental label application is still in review by USEPA.

Finally, WS currently has the Brodifacoum-25W Conservation Section 3 label registered in the 

state of Alaska, although it has not been used in Alaska since USFWS used it on St. Paul Island 

in 2008.

Since 2011, APHIS also registered a supplemental label (now expired) for USFWS and IC to 

eradicate black rats (R. rattus) from Palmyra Island (Brodifacoum-25W Conservation; 1st attempt 

in 2011 succeeded), and two supplemental labels (now expired) for USFWS and IC to eradicate 

black rats from Desecheo Island (Brodifacoum-25D Conservation; 1st attempt in 2012 failed, 2nd

attempt in 2016 succeeded).

Although WS primarily uses brodifacoum for island conservation projects to eradicate invasive 

rodents, WS does have minor use of brodifacoum outside of island conservation. Between 

FY2016 and FY2020, WS applied an annual average of 1.6 pounds of Talon® Weatherblok® XT 

(Syngenta Crop Protection, LLC, USEPA Registration Number: 100-1055) to control the Norway 

rat near manmade structures in Tennessee. WS also sold an annual average of 37.8 pounds of 

Talon® Weatherblok® XT to cooperators for the control of house mice and Norway rats in Texas.

Table 1 APHIS brodifacoum products and supplemental labels for island conservation projects

since 2011 (current and expired) and other minor non-island conservation uses of a non-APHIS 

product.

Product Bait Application Rate Use Pattern

Product name: 

Brodifacoum-25W 

Conservation

Label type: Section 3 label

USEPA Registration No.: 

56228-36

Label version: Nov. 12, 

2019

Formulation: 0.0025% w/w 

brodifacoum, 0.9975% w/w 

other ingredients1

Hand baiting application rates

depend on the application method 

and whether treating for rats or 

mice.

The maximum amount of bait 

applied by hand broadcast and 

aerial broadcast applications is 16

pounds (lb.)/acre (18 kilogram 

(kg)/hectare (ha)). A second 

application can be made 5 to 7 

days after the first application at 

no more than 8 lb./acre (9 kg/ha).

Control or eradicate invasive rodents

in wet climates on islands or vessels 

for conservation purposes.

Hand spot baiting methods:

• Tamper-resistant bait stations at all 

use sites on the label

• Burrow baiting in uninhabited noncrop areas

• Bait bolas (sachets) on uninhabited 

grounded or in peril of grounding 

vessels; canopy of trees and 

shrubs in non-crop areas

Broadcast applications in 

uninhabited areas but not on 

vessels:
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Product Bait Application Rate Use Pattern

• Aircraft

• Ground-based mechanical 

equipment

• Gloved hand

Product name:

Brodifacoum-25D 

Conservation 

Label type: Section 3 label

USEPA Registration No.: 

56228-37

Label version: Nov. 12, 

2019

Formulation: 0.0025% w/w 

brodifacoum, 0.9975% w/w 

other ingredients2

Hand baiting application rate 

depends on the application 

method and whether treating for 

rats or mice.

The maximum amount of bait 

applied by hand broadcast and 

aerial broadcast applications is 16 

lb./acre (18 kg/ha). A second 

application can be made 5 to 7 

days after the first application at 

no more than 8 lb./acre (9 kg/ha).

Control or eradicate invasive rodents

in dry climates on islands or vessels 

for conservation purposes.

Hand spot baiting methods:

• Tamper-resistant bait stations at all 

use sites on the label

• Burrow baiting in uninhabited noncrop areas

• Bait bolas (sachets) on uninhabited 

grounded or in peril of grounding 

vessels; canopy of trees and 

shrubs in non-crop areas

Broadcast applications in 

uninhabited areas but not on 

vessels:

• Aircraft

• Ground-based mechanical 

equipment

• Gloved hand

Product name: Talon®

Weatherblok® XT, 

Syngenta Crop Protection, 

LLC

Label type: Section 3 label

USEPA Registration 

No.100-1055

Label version: Feb. 13, 

2015

Formulation: 0.005% w/w 

brodifacoum, 99.995% w/w 

other ingredients

Norway and roof rats:

• Apply 4–22 [(20 g (0.7 oz.)] 

blocks (usually at intervals of 

15–30 ft) per placement

House mice:

• Apply 1 bait block per 

placement. Space placements 

at intervals of 8–12 feet. Two 

blocks may be needed at points 

of very high mouse activity

Control of Norway rats (R. 

norvegicus), roof (black) rats (R. 

rattus), and house mice (M. 

musculus) in and within 100 feet of 

man-made structures.

Tamper-resistant bait stations 

required in:

• Residential structures

• USDA-inspected facilities

• In treatment areas where children, 

pets, non-target mammals, or birds 

may access the bait

Bait stations required for all aboveground, outdoor applications 

Product name: 

Brodifacoum-25D 

Conservation

Label type: Supplemental 

label for use on Midway 

Atoll National Wildlife 

Refuge (Sand Island)

USEPA Registration No. 

56228-37

Hand application rate depends on 

the application method.

The maximum amount of bait 

applied by hand broadcast and/or 

aerial broadcast applications may 

not exceed 71.3 lb./acre (79.9 

kg/ha) under this supplemental 

label. This maximum application 

rate may be locally exceeded 

along adjacent borders of parallel 

swaths. A second broadcast 

application can be made at the 

Eradicate house mice (Mus 

musculus) on Midway Atoll National 

Wildlife Refuge’s Sand Island.

Hand spot baiting methods:

• Bait stations

• Bait trays and bait bolas

Broadcast applications methods are 

the same as the parent label above.
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Product Bait Application Rate Use Pattern

Expiration date: Dec. 25, 

2025

Formulation: 0.0025% w/w 

brodifacoum, 0.9975% w/w 

other ingredients2

same maximum rate 14 to 30 

days after the first application. An 

additional middle application at 

the same maximum rate can be 

made 7 to 12 days following the 

first application in cases of high 

bait disappearance after the first 

application.

Product name: 

Brodifacoum-25W 

Conservation

Label type: Supplemental 

label for use on Wake Atoll

USEPA Registration No.: 

56228-36 

Label expiration: Dec. 31, 

2026

Formulation: 0.0025% w/w 

brodifacoum, 0.9975% w/w 

other ingredients1

Hand baiting application rate 

depends on the application 

method.

The maximum amount of bait 

applied by hand broadcast and/or 

aerial broadcast applications to 

Wake Atoll in the primary baiting 

operation may not exceed 135 

lb./acre (150 kg/ha) under this 

supplemental label; This 

maximum application rate may be 

locally exceeded along adjacent 

borders of parallel swaths. A 

second broadcast application at 

the same application rate can be 

made 14 to 28 days after the first 

application. An additional middle 

application can be made 5 to 14 

days following the first application 

in cases of high bait 

disappearance after the first 

application. 

Eradicate Polynesian (Pacific) rats 

(Rattus exulans) and other invasive 

rodents on Wake Atoll.

Hand spot baiting methods the same 

as the parent label above, with the 

inclusion of:

• Enclosed bait stations (either tubes 

or bait boxes with lids)

• Elevated and floating bait stations

• Bait trays

Broadcast application methods the 

same as the parent label above, with 

the inclusion of:

• Unmanned aerial vehicles (UAV)

*In review with USEPA

Product name: 

Brodifacoum-25D 

Conservation

Label type: Supplemental

label for use on Savana 

Island, St. Thomas, U.S. 

Virgin Islands

USEPA Registration No.: 

56228-37

Proposed expiration date: 

Dec. 31, 2029

Formulation: 0.0025% w/w 

brodifacoum, 0.9975% w/w 

other ingredients2

Hand application rate depends on 

the application method.

The maximum amount of bait 

applied by hand broadcast and/or 

aerial broadcast applications may 

not exceed 26.76 lb./acre (30

kg/ha) under this supplemental 

label. This maximum application 

rate may be locally exceeded 

along adjacent borders of parallel 

swaths. A second broadcast 

application at the same maximum 

rate can be made 14 to 28 days 

after the first application. 

Eradicate black rats (Rattus rattus)

on Savana Island, St. Thomas, U.S. 

Virgin Islands.

Hand spot baiting methods the same 

as the parent label above, with the 

inclusion of:

• Enclosed bait stations (either tubes 

or bait boxes with lids)

• Bait trays and bait sachets

Broadcast application methods the 

same as the parent label above, with 

the inclusion of:

• Unmanned aerial vehicles

Product name: 

Brodifacoum-25D 

Conservation 

Hand application by bait stations

up to 16 oz (454 g) per bait 

station spaced 160 ft (50 m) 

apart. Check and refill bait 

Eradicate roof (black) rats (R. rattus)

on Desecheo Island.

Hand spot baiting methods:

• Bait stations
9

Product Bait Application Rate Use Pattern

Label type: Supplemental 

label for use on Desecheo 

Island, Puerto Rico

USEPA Registration No.: 

56228-37

Expiration date: Apr. 30, 

2014

Formulation: 0.0025% w/w 

brodifacoum, 0.9975% w/w 

other ingredients2

stations at least every 7 days for 

the first 6 weeks of the operation.

The broadcast application rate

(applied by hand broadcast or

aerial broadcast) is to be targeted 

at 16 lb./acre (18 kg/ha) on the 

ground after adjusting the sow 

rate for the 3-dimensional surface 

of the island. A second 

application is to be targeted at 8 

lb./acre (9 kg/ha) on the ground 

with the interval between 

applications timed to maximize 

the probability of baiting weanling 

rats that survived the first 

application.

Broadcast applications:

• Aerial

• Gloved hand

Product name: 

Brodifacoum-25W 

Conservation

Label type: Supplemental 

label for use on Palmyra 

Atoll

USEPA Registration No.: 

56228-36 

Expiration date: Jul. 31, 

2014

Formulation: 0.0025% w/w 

brodifacoum, 0.9975% w/w 

other ingredients1

Hand application rate depends on 

application method.

For broadcast (air, ground-based 

equipment, by hand) application, 

two broadcast applications may 

be made during the initial 

eradication attempt. 

• The first application is to be 

targeted at 71.3 Ib./acre (80 

kg/ha) and will not exceed 80.2 

Ib./acre (90 kg/ha). 

• The second application, is to be 

targeted at 66.8 Ib./acre (75

kg/ha) and will not exceed 80.2 

Ib./acre (90 kg/ha).

Eradicate black rats (R. rattus) on 

Palmyra Atoll.

Hand spot baiting methods:

• Bait stations

• Canopy baiting

Broadcast applications:

• Hand

• Aerial

Product name: 

Brodifacoum-25W 

Conservation

Label type: Supplemental 

label for use on Wake Atoll

USEPA Registration No.: 

56228-36

Expiration date: Sep. 1, 

2014

Formulation: 0.0025% w/w 

brodifacoum, 0.9975% w/w 

other ingredients1

Hand application rate depends on 

application method (bait stations 

or canopy baiting).

The broadcast application rate 

(applied by hand broadcast or 

aerial broadcast) is to be targeted 

at 16 lb./acre (18 kg/ha). A 

second application is to be 

targeted at 8 lb./acre (9 kg/ha) 

with the interval between 

applications timed to maximize 

the probability of baiting weanling 

rats that survived the first 

application.

Eradicate Polynesian (Pacific) rats 

(R. exulans) and Asian house rats 

(R. tanezumi) on Wake Atoll.

Hand spot baiting methods:

• Bait stations

• Canopy baiting

Broadcast applications:

• Aerial

• Gloved hand

Product name: 

Brodifacoum-25D 

Conservation 

Hand application by bait stations 

up to 16 oz (454 g) per bait 

station spaced 160 ft (50 m) 

apart. Check and refill bait 

stations at least every 7 days

during the operation.

Eradicate roof (black) rats (R. rattus)

on Desecheo Island.

Hand spot baiting methods:

• Bait stations
10

Product Bait Application Rate Use Pattern

Label type: Supplemental 

label for use on Desecheo 

Island, Puerto Rico

USEPA Registration No.: 

56228-37

Expiration date: Nov. 23, 

2020

Formulation: 0.0025% w/w 

brodifacoum, 0.9975% w/w 

other ingredients2

For broadcast applications (aerial 

or hand), 2 application periods 

with 3 applications/period allowed 

for the eradication attempt:

• An application targeting the 

coastal zone of the island will 

be applied at a rate of 27

lb./acre (30 kg/ha), using a 

deflector to direct bait away 

from the water’s edge.

• An application targeting the 

interior island and offshore 

islets will be applied at a rate of 

27 lb./acre (30 kg/ha).

• An additional application of bait 

targeting the coastal/interior 

zone overlap, valley floors and 

interior cliff faces will be applied 

at a rate of 13 lb./acre (15

kg/ha).

Broadcast applications:

• Aerial

• Gloved hand

1 Brodifacoum-25W Conservation is formulated for use in wet climates. 2 Brodifacoum-25D Conservation is formulated for use in dry climates.

References: (USEPA 2011;2015;2019a;b;2021;2022b)

The ground and aerial broadcast rates described in the current and proposed Brodifacoum-25D

Conservation and Brodifacoum-25W Conservation supplemental labels may be exceeded under 

certain scenarios. For ground broadcast applications there may be exceedance of rates along 

edges of areas missed or excluded during application aerial broadcast applications. The 

supplemental labels also allow for bait application overlap from aerial broadcast applications in 

flight lines to ensure thorough coverage to all intended areas. The extent of overlap will vary based 

on site-specific conditions. Overlap may occur in the coastal/interior overlap zone and may also

occur along borders of parallel swaths, at the end of swaths where they intercept swaths created 

by shoreline or other perimeter baiting, and from back baiting. Applicators should minimize areas 

where applications overlap but should also ensure that they are baiting all areas sufficiently to 

maximize efficacy.

The Brodifacoum-25D Conservation and Brodifacoum-25W Conservation formulations contain 

0.0025% w/w brodifacoum; the Talon Weatherblok XT formulation contains 0.005% w/w 

brodifacoum. The concentration of the brodifacoum pellets that WS will use for future island rodent 

eradication projects may change as WS develops or uses alternate formulations registered by 

other registrants. While the percentage of active ingredient in pellets may increase in future 

formulations the range of active ingredient application rates per acre is not anticipated to exceed 

those maximum rates described in this risk assessment. Any increases in the amount of active 

ingredient applied per acre would result in a need for the lead federal agency for the project to

reevaluate the risk to human health and ecological resources.

2 PROBLEM FORMULATION

The following sections discuss physical and chemical properties, environmental fate, and hazard 

identification for brodifacoum. 
11

2.1 Physical and Chemical Properties

Brodifacoum (synonyms: 3-[3-(4'-Bromo-[1,1'-biphenyl]-4-yl)-1,2,3,4-tetrahydro-1-naphthalenyl]-

4-hydroxy-2H-1-benzopyran-2-one or 3-[(1RS,3RS;1RS,3SR)-3-(4’-bromobiphenyl-4-yl)-1,2,3,4-

tetrahydro-1-naphthyl]-4-hydroxycoumarin; chemical formula: C31H23BrO3; CAS No.: 56073-10-0) 

is an organic compound with a molecular weight of 523.43 grams per mole (g/mol) and a 

molecular structure shown in Figure 1 (USEPA 2016c, NCBI 2023).

Figure 1. Chemical structure for brodifacoum.

Technical brodifacoum is a cream colored, fine, powdery solid with a melting point of 232°Celsius 

(C). Under field conditions, brodifacoum is non-volatile. Brodifacoum’s estimated vapor pressure

is 1.11 x 10-18 mmHg (torr) at 25°C or less than 10-8 torr at 20°C. Brodifacoum has a calculated 

Henry’s Law constant of 2.012 x 10-16 atm-m3

/mole at 25°C, or less than 10-8 atm-m3/mole at pH 

7.4 and 20°C. Brodifacoum’s bulk density is 1.42 g/centimeter3 (cm3

) at 25°C. Brodifacoum has 

low water solubility in acidic to neutral waters with increased solubility at alkaline pH values. The 

water solubility for brodifacoum ranges from 0.0038 milligrams (mg)/Liter (L) at pH 5.2 to 0.24 

mg/L at pH 7.4 to 10.0 mg/L at pH 9.3 buffered water at 20°C. Brodifacoum has a high estimated 

n-octanol-water partition coefficient (Kow) of 3.16 x 108 (log Kow of 8.5) (USEPA 2016a, NCBI 

2023). The soil adsorption coefficient (Koc) value was 9,155 L/g-oc (organic carbon) at pH 7.1-7.6 

(USEPA 2020b).

2.2 Environmental Fate

Environmental fate describes the processes by which chemicals move and degrade in the 

environment. The environmental fate processes include 1) persistence, degradation, and mobility 

in soil; 2) movement to air; 3) migration potential to groundwater and surface water; 4) degradation 

in water; and 5) plant uptake.

Brodifacoum is relatively persistent in soil with a degradation half-life in soil of 157 days in sandy 

clay loam soil at 21 ̊C (USEPA 1998). Brodifacoum is immobile in soil with a Koc of >9,155 L/g-oc

(USEPA 2016c;2020b). Leaching studies in aged columns of sand, sandy clay loam, silty clay,

and clay also indicated that brodifacoum is immobile in soil (USEPA 2016c). Brodifacoum has a 

low migration potential to groundwater and surface water (USEPA 2016c). Brodifacoum is not 

readily or inherently biodegradable (USEPA 2016c).
12

Brodifacoum has a very low vapor pressure (1.11 X 10-18 mmHg at 25°C) and a low Henry’s Law 

constant value (estimated 2.012 x 10-16 atm-m3

/mol), suggesting a low potential for volatilization 

into the atmosphere from soil and water (USEPA 2016c). 

Brodifacoum is stable to hydrolysis at pH 5, 7, and 9 (USEPA 2016c). Brodifacoum has the 

potential to bioaccumulate/bioconcentrate in aquatic environments based on its high Kow (3.16 x 

108

). The estimated fish bioconcentration factor is 2,450 L/kilogram (kg) wet-weight, with a very 

slow biotransformation rate (a half-life of 351 days) (USEPA 2016c).

The potential uptake of brodifacoum by plants is low. Most of the bait is expected to be removed 

by the target species, reducing the amount of brodifacoum available for degradation and leaching 

into the soil. Brodifacoum is not expected to be available for plant uptake since it binds to soil 

organic matter rendering it unavailable for uptake (IPCS 2005). 

The primary route of dissipation or transportation of brodifacoum appears to be through a food 

chain where birds, mammals, or other organisms consume bait products, carry the intact chemical 

within their bodies, and move to offsite locations. During the period of days from exposure to 

mortality, these poisoned animals become secondary sources for predators and scavengers 

(USEPA 2016c).

2.3 Hazard Identification 

Brodifacoum is an anticoagulant that targets the hematological system with coagulopathy 

(impairment of clotting) (IPCS 1992, NCBI 2023). The most sensitive toxicity indicator is 

prothrombin time measurements of bleeding (USEPA 2016a). Toxicity signs are typically 

hemorrhaging, followed by death. Symptoms in less severe brodifacoum poisoning incidents 

include excessive bruising, nose and gum bleeding, and blood in the urine and feces (IPCS 2005). 

In more severe cases, symptoms may include bleeding from several organs within the body,

leading to shock and possible death (IPCS 2005).

As a second-generation anticoagulant, brodifacoum is more acutely toxic in a single feeding 

compared to first-generation anticoagulants and is more persistent in biological tissue. APHIS’ 

two bait formulations contain 0.0025% w/w brodifacoum. Pesticide label statements regarding the 

human health effects of these bait formulations based on toxicity studies include “Harmful if 

swallowed. Causes moderate eye irritation. Avoid contact with eyes, skin, or clothing.” (USEPA 

2019a;b).

In 2008, USEPA published their Risk Mitigation Decision (RMD) for Ten Rodenticides, with a 

number of new label mitigations intended to minimize exposure to children and ecological 

systems, including wildlife (USEPA (2008). In this decision document, four second-generation 

anticoagulants, including brodifacoum, were prohibited for use in general consumer residential 

products. 

The USEPA Health Effects Division (HED) completed an updated analysis of exposure incidents 

for 11 anticoagulant and non-anticoagulant rodenticides with outdoor uses, which included 

brodifacoum, and summarized exposure incidents since the RMD was published (USEPA 

2020a;2022a). USEPA reviewed the Incident Data System (IDS), the American Association of 

Poison Control Centers (AAPCC), the Center for Disease Control’s National Institute for 

Occupational Safety and Health (NIOSH) Sentinel Event Notification System for Occupational 

Risk (SENSOR)-Pesticides database, and the California Pesticide Illness Surveillance Program 

(PISP) for rodenticide human exposure incidents, including exposure to brodifacoum (USEPA 
13

2022a). The USEPA summary of rodenticide incidents in the AAPCC was not analyzed by 

rodenticide active ingredient but by first- and second-generation anticoagulant rodenticides.

As per the USEPA HED (USEPA 2022a), the number of second-generation (not limited to 

brodifacoum) anticoagulant rodenticide incidents reported in the IDS (2009 to 2018) decreased 

by 79% (from 164 incidents in 2009 to 34 incidents in 2018) and in the AAPCC (2004 to 2017) 

decreased by 70%. In the AAPCC, the total number of reported child exposures was reduced by 

46% between 2011 and 2017 (USEPA 2022a).

In the Main IDS, from January 1, 2015, to July 12, 2019, there were 15 incidents reported that 

involved brodifacoum; 13 of which involved only brodifacoum and two involved brodifacoum and 

multiple active ingredients. Twelve incidents were classified as moderate severity, and one 

incident was classified as major severity (USEPA 2022a). In the Aggregate IDS during the same 

period, there were 85 incidents reported involving brodifacoum and these were classified as minor 

severity.

USEPA (2022a) queried the SENSOR database from 2011–2015 and found two instances of 

brodifacoum incidents. In 2014, one incident involved brodifacoum where the applicator 

accidentally ingested the product when he forgot to put away his food prior to application. He 

experienced muscle weakness. In 2011, one incident involved an agricultural worker cleaning a 

barn; he believed he may have swallowed bait dust. He experienced headache, nausea, and 

vomiting. These incidents occurred using a product line named d-Con, brodifacoum baits that 

were cancelled in 2015. 

An additional literature review identified human exposure cases from ingestion of brodifacoum 

with symptoms of generalized ecchymosis, abortion, flank pain, and hematuria followed by 

epistaxis, gum bleeding, and persistent bleeding for more than two months (NCBI 2023). A case 

study of brodifacoum exposure in humans reported persistent coagulopathy that lasted 

approximately one year despite long-term treatment with large dosages of oral phytonadione 

(vitamin K1), even when brodifacoum was undetectable in the serum (Underwood et al. 2014). 

One case reported a woman with hemoptysis (coughing up blood) and dyspnea (shortness of 

breath) following inhalation exposure; she entered an unventilated ceiling space that contained 

brodifacoum, which was placed approximately two years prior (Love et al. 2019). She estimated 

she was in the space for about 4 minutes; while there, she noticed the outer coating on the pellets 

was degraded, showing brodifacoum powder.

WS has had no human adverse incident reports from its limited use of brodifacoum since 2007 

for WS personnel or the public.

2.3.1 Mechanism of Action and Metabolism

Brodifacoum is a vitamin-K antagonist that disrupts normal blood-clotting mechanisms and 

induces capillary damage, leading to death from hemorrhage (USEPA 2004).

Brodifacoum is absorbed through the gastrointestinal tract, skin, and respiratory system (IPCS 

2005). The liver is the main organ of accumulation and storage (IPCS 2005). Metabolism studies 

measuring recovery of radioactivity following a single oral administration to rats of 14C-labeled 

brodifacoum (10 mg/kg-bodyweight (bw)) indicate that considerable radioactivity (approximately 

64% of the administered dose) was absorbed and retained in the liver (15%), carcass (43%), and 

bile (6%) after 48 hours (USEPA 1998;2016c). “After a single oral dose to rats, liver concentrations 

remained high and relatively constant for 96 hours. Elimination from the liver is slow and biphasic 

with an initial rapid phase lasting from 2 to 8 days after dosing and a slower terminal phase with 
14

an elimination half-life of 130 days.” (IPCS 2005). Following oral administration, brodifacoum is 

mostly eliminated through feces (IPCS 2005). Brodifacoum has mainly been found as an 

unchanged compound in feces (IPCS 2005). Approximately 36% of the administered dose was 

recovered in the feces as unabsorbed. The major (and only identified) metabolite of brodifacoum 

in bile was the glucuronide conjugate (USEPA 1998). In patients accidentally poisoned with 

brodifacoum, the plasma half-life was approximately 16–36 days (IPCS 2005).

2.3.2 Toxicity

The acute oral, dermal, and inhalation median lethality values (LD50 and LC50) in rats and rabbits

indicate that technical brodifacoum is highly toxic (Category I) and is a mild irritant (Category III)

when in contact with eyes (Table 2). Dermal irritation was not tested because of its high dermal 

toxicity. The dermal sensitization study shows that brodifacoum is not a skin sensitizer in guinea 

pigs.

A 0.25% w/w brodifacoum manufacturing use concentrate product tested in toxicology registration 

studies called Brodifacoum Formulation Concentrate is moderately toxic (Category II) based on 

the oral LD50 and low toxic (Category III) based on the dermal LD50 (Table 2). Dermal contact can 

result in severe skin burns or an allergic reaction. This product is 100 times more concentrated 

than the brodifacoum bait formulations (0.0025% or 0.005%) that WS uses. 

Accordingly, the 0.0025–0.005% w/w baits are much less acutely toxic compared to the technical 

and concentrate formulations (Category IV) (Table 2). The Brodifacoum-25D Conservation and 

Brodifacoum-25W Conservation safety data sheets (Bell Laboratories 2015b;a) states that 

contact exposure to the eye will cause moderate irritation.

Table 2. Acute toxicity values of technical brodifacoum used by USEPA to assess acute risk to 

human health, as well as acute toxicity values for brodifacoum formulations.

Test Test 

Species

Technical 

Brodifacoum

0.25% w/w

Brodifacoum 

Formulation 

Concentrate

Talon®

Weatherblok®

XT 0.005% 

w/w 

Brodifacoum

APHIS 0.0025%

w/w

Brodifacoum 

Formulations

Acute Oral 

(LD50)

Rat 0.418 mg/kg-bw

(M)

0.561 mg/kg-bw

(F) 

0.490 mg/kg-bw 

(both sexes)

163 mg/kg-bw (M) 

152 mg/kg-bw (F)

>5,000 mg/kgbw>5,001 mg/kgbw

Acute Dermal 

(LD50)

Rabbit

or Rat

5.21 mg/kg-bw (M)

3.16 mg/kg-bw (F)

(rabbit)

>2,000 mg/kg-bw

(M, F) (rat)

Not available >5,001 mg/kgbw (rat)

Acute 

Inhalation 

(LC50)

Rat 4.86 μg/L(M)

3.05 μg/L (F)

Not available Not available Not available

Eye Irritation Rabbit Minor eye 

irritation, clearing 

by day 7

Iritis clearing by 48 

hours

Not irritating to 

eyes

Not irritating to 

eyes

Dermal 

Irritation

Rabbit

or Rat

Not available Not irritating to 

skin

Not irritating to 

skin

Not irritating to 

skin
15

Test Test 

Species

Technical 

Brodifacoum

0.25% w/w

Brodifacoum 

Formulation 

Concentrate

Talon®

Weatherblok®

XT 0.005% 

w/w 

Brodifacoum

APHIS 0.0025%

w/w

Brodifacoum 

Formulations

Dermal 

Sensitization

Guinea 

Pig

Non sensitizer Not a sensitizer Not available Not a sensitizer

M = male, F = female

References: (USEPA 1998, Bell Laboratories 2015b;a, USEPA 2016c)

2.3.3 Sub-chronic/Chronic Toxicity

During their initial registration review workplan for brodifacoum, USEPA (2016a) determined that 

a 21-day dermal toxicity study in rats (Guideline 870.3200) and a 28-day inhalation toxicity study 

in rats (Guideline 870.3465) would be required to maintain brodifacoum registrations, including

prothrombin and activated partial thromboplastin time measurements (pre-exposure, and on days 

7, 14, and 21/28 of exposure). However, later during registration review, USEPA (2020a) waived 

these data requirements for the subchronic dermal and inhalation toxicity studies based on a 

weight-of-evidence approach using the known properties of brodifacoum. Instead, USEPA 

assumed toxicity for these routes of exposure given that the mode of action and acute toxicity 

profile are well understood.

2.3.4 Developmental and Reproductive Effects

Brodifacoum developmental toxicity studies are available for rats and rabbits. A range-finding 

study reported 100% maternal mortality at a higher dose of 0.05 mg/kg-bw/day. The subsequent 

developmental toxicity study in rats at 0, 0.001, 0.01, or 0.02 mg/kg-bw/day did not report 

developmental effects at the highest dose tested (developmental toxicity no observable adverse 

effects level (NOAEL) of 0.02 mg/kg-bw/day). The study reported a maternal lowest observable 

adverse effect level (LOAEL) of 0.01 mg/kg-bw/day based on the finding of blood in the uteri at 

0.01 and 0.02 mg/kg-bw/day. The maternal toxicity NOAEL in the study was 0.001 mg/kg-bw/day. 

The rabbit developmental study at 0, 0.001, 0.002, and 0.005 mg/kg-bw/day reported significant 

maternal toxicity (mortality and internal hemorrhage) as well as implantation loss at the maternal 

toxicity LOAEL of 0.005 mg/kg-bw/day. The LOAEL for developmental toxicity was also 0.005 

mg/kg-bw/day based hemorrhagic appearance of fetuses from the three litters available for 

evaluation. The NOAEL was 0.002 mg/kg-bw/day for both maternal and developmental toxicity. 

There was no qualitative or quantitative sensitivity seen in the developmental rat or rabbit studies 

(USEPA 2016a).

USEPA (2016a) waived the requirement for a two-generation reproductive toxicity study in rats 

based on a weight-of-evidence approach and considering the available hazard and exposure 

information.

2.3.5 Neurotoxicity and Immunotoxicity Effects

USEPA (2016a) also waived the acute and subchronic neurotoxicity considering the available 

toxicity and exposure information. 

A literature review did not identify studies indicating the potential for neurotoxicity from 

brodifacoum exposure. Kalinin et al. (2017) reported the direct toxic effects of brodifacoum on 

neurons and glia in an in vitro study using an enriched culture of rat cerebellar neurons and cortical 

astrocytes. After overnight incubation in the study, brodifacoum induced significant cell death in 

neurons and astrocytes at molar concentrations of 3 micromolar (μM) and 30 μM, respectively. 
16

2.3.6 Carcinogenicity and Mutagenicity

A literature search did not identify carcinogenicity studies using brodifacoum. USEPA (2016a)

determined that chronic and/or carcinogenicity studies are not required based on brodifacoum's

non-food uses and the mutagenicity studies' negative findings. 

USEPA (2016a) concluded that brodifacoum is not a mutagen based on the negative results of 

three mutagenicity studies (a bacterial reverse mutation assay, a mouse micronucleus assay, and 

a human lymphocyte assay). In the Ames assay with Salmonella strains, brodifacoum was 

negative for inducing reverse gene mutation at the histidine locus at levels up to 5,000 micrograms 

(μg)/plate with and without metabolic S-9 activation. The mouse micronucleus assay found that 

brodifacoum did not induce a clastogenic and/or aneugenic effect in either sex at an 

intraperitoneal dose of 0.3 mg/kg-bw. A higher dose (0.5 mg/kg-bw) in a preliminary study caused 

70% mortality. The in vitro cytogenetic assay using human lymphocytes found that brodifacoum 

was not cytogenic (no increase in the frequency of lymphocyte chromosomal aberrations).

Overall, USEPA concluded that brodifacoum has little to no genotoxic activity.

2.3.7 Endocrine System Effects

An Endocrine Disruptor Screening Program (EDSP) was developed to characterize endocrine 

activity in commercial products, pesticides, and environmental contaminants (USEPA 2023b). 

EDSP uses a two-tier risk characterization approach consisting of screening candidate 

compounds for estrogen, androgenic, and thyroid receptor activity and quantifying their impact on 

environmental and human health (USEPA 2023b). Before 2012, Tier 1 screening involved five in 

vitro and six in vivo assays (Browne et al. 2015). To address the growing need for a more rapid 

but equally comprehensive review of thousands of candidate compounds, the EDSP revised Tier 

1 screening to include computational endocrine activity models and high-throughput assays. Tier 

2 testing data characterizes the endocrine-related health effects, dose response, and health risks 

of candidate compounds and substances. Although brodifacoum is listed in the EDSP Universe 

of Chemicals (USEPA 2012;2023a), brodifacoum was not screened for estrogen receptor 

bioactivity. 

A literature search did not identify any mammalian studies indicating the potential of brodifacoum 

to affect the endocrine system. Brodifacoum is not among the group of pesticide active ingredients 

on the initial and secondary lists to be screened under the USEPA EDSP (USEPA 2024b). 

However, both lists were generated based on exposure potential and not whether the pesticide is 

a known or likely chemical to disrupt the endocrine system (USEPA 2024b). Brodifacoum is not 

on the European Union (EU) list of chemicals with the potential to impact the endocrine system 

(ECHA 2023, The Danish Environmental Protection Agency 2024). The EU list includes three 

categories: Category 1 – endocrinal effect recorded at least on one type of animal; Category 2 –

a record of biological activity in vitro leading to disruption; and Category 3 – not enough evidence 

or no evidence data to confirm or disconfirm endocrinal effect of tested chemicals (Hrouzková 

and Matisova 2012).

2.3.8 Toxicity of Other Ingredients

The remaining 99.995 and 99.9975% w/w of the brodifacoum bait product formulations are “other” 

or inert ingredients (e.g., (USDA APHIS 2009, USEPA 2019a;b, HACCO 2021). The identity and

safety profile of inert ingredient contents of brodifacoum formulations are not presented on labels 

or safety data sheets. These ingredients are considered confidential business information and not

generally available to the public. However, they still must be approved inert ingredients for nonfood use pesticides by USEPA (2023c).
17

3 DOSE-RESPONSE ASSESSMENT

3.1 Human Health Dose-Response Assessment

A dose-response assessment evaluates the dose levels (toxicity criteria) for potential human 

health effects, including acute and chronic toxicity. USEPA did not establish a tolerance for 

brodifacoum because there are no registered food or feed uses. The maximum contaminant level 

has not been established for drinking water. USEPA did not establish an oral reference dose for 

brodifacoum because USEPA does not believe that the potential exists for significant oral

exposure to occupational workers or to the public from incidental exposures from food or drinking 

water. 

For occupational dermal exposure to brodifacoum baits, USEPA (2016a) proposed using a 

NOAEL of 2 μg/kg-bw/day based on prothrombin time and a LOAEL of 5 μg/kg-bw/day from the 

developmental study in rabbits as the endpoint in their short- and intermediate-term dermal 

exposure risk evaluation. The reported LOAEL in the study was based on 75% mortality 

associated with hemorrhage in pregnant females. The occupational level of concern (LOC) for 

margin of exposure (MOE) was 1,000 using an uncertainty factor (UF) of 10x for extrapolation 

from animal to human (interspecies), an UF of 10x for potential variation in sensitivity among 

members of the human population (intraspecies), and an UF of 10x to account for the absence of 

key data (i.e., lack of a critical dermal study). USEPA used a dermal short- and intermediate-term 

dermal absorption factor of 5% to be conservative based on the available data.

However, later in registration review, USEPA determined that a quantitative risk assessment was 

not necessary for occupational dermal and inhalation exposure, as any potential exposure may 

result in adverse effects and potential risks of concern (USEPA 2020a). USEPA proposed to 

require additional personal protective equipment (PPE) on labels to minimize occupational 

exposure in the future (USEPA 2020a).

In another risk assessment, the average fatal dose for a (60 kg-bw) man was estimated to be 15 

mg brodifacoum or 300 g of 0.005% bait (IPCS 2005).

3.2 Ecological Effects Analysis

This section summarizes available brodifacoum toxicity data for aquatic and terrestrial species.

Data searches included the primary literature, unpublished reports, and databases to find 

representative effects data for aquatic and terrestrial species. 

3.2.1 Aquatic Effects Analysis

Brodifacoum is considered highly toxic to warmwater and coldwater fish species. Acute LC50 

values range from 0.033 mg/L for the rainbow trout (Oncorhynchus mykiss) to 0.15 mg/L for 

bluegill (Lepomis macrochirus) in 96-hour acute exposure toxicity tests (Table 3). Toxicity data 

for marine species is limited; however, available data for freshwater fishes shows that 

brodifacoum could be toxic to marine fishes. Riegerix et al. (2020) exposed the marine fish 

species, red-toothed triggerfish (Odonus niger) and black triggerfish (Melichthys niger), to 

brodifacoum using a single intraperitoneal injection. These types of exposures have limited use 

in risk assessments due to method of administration of the test chemical, but the study 

demonstrated that brodifacoum toxicity is similar between marine and freshwater fish species 

when dosed using similar methods. The study originally tried oral exposures; however, neither 

fish species would consume bait pellets. Fish were also dosed with brodifacoum using oral 

gavage but regurgitated the bait pellets. This suggests that these fish species will not 

preferentially consume bait pellets that inadvertently enter the marine environment. 
18

Sublethal effects on fish from brodifacoum exposure have also been observed in short- and longterm laboratory toxicity testing. Wu et al. (2023) reported adverse effects on zebrafish, Danio 

rerio, in six and 96-hour exposures to brodifacoum at 0.8 mg/L. Morphological impacts were noted 

at 0.8 mg/L in the 96-hr exposures. Effects noted at 0.8 mg/L in both exposure durations include 

decreases in heart rate, survival, body length, and spontaneous movements. No significant effects 

were noted at the 0.2 and 0.4 mg/L concentrations. Driessnack et al. (2023) reported lethal and 

sublethal impacts to Coho salmon (Oncorhynchus kisutch) in 76-day exposures to 25 mg/kg 

brodifacoum bait pellets. Coho salmon embryos were exposed to brodifacoum pellets from 

fertilization through hatching in a flow-through water system. In the presence of brodifacoum 

pellets there were significant adverse effects to embryo and alevin survival and development, with 

pronounced cranial hemorrhaging. 

Brodifacoum is considered highly toxic to aquatic invertebrates based on the available toxicity 

data for the freshwater cladoceran, Daphnia magna. The reported median effective 

concentrations (EC50) in a 48-hour exposure range from 0.24 to 0.88 mg/L (USEPA 1991, EU 

2016) (Table 3). Marine invertebrate toxicity data is unavailable; however, brodifacoum is 

considered toxic to marine invertebrates, including corals, based on available studies for 

freshwater invertebrates. Available toxicity data for other pesticides show that coral sensitivity is 

within the range of other aquatic freshwater and marine invertebrate toxicity data for various 

insecticides, herbicides, and fungicides (van Dam et al. 2011, Flores et al. 2020). Barkman and 

Richmond (2022) reported sublethal impacts to rice coral, Montipora capitata, exposed to bait 

pellets after exposure to 10 and 100 μg/L brodifacoum. Sublethal effects were not observed at 

the lowest test concentration of 1 μg/L. 

Table 3. Brodifacoum acute toxicity in aquatic species.

Test Species Scientific Name LC50/EC50 (mg a.i./L) Reference

Freshwater Cladoceran Daphnia magna 0.24–0.88 (USEPA 1991, EU 2016)

Rainbow trout Oncorhynchus mykiss 0.033 (USEPA 1991)

Bluegill Lepomis macrochirus 0.15 (USEPA 1991)

Brodifacoum is considered toxic to algae with a reported EC50 of 0.04 mg/L for the freshwater 

green algae (Raphidocelis (formerly Pseudokirchneriella) subcapitata). The effects were based 

on negative impacts to growth in a 72-hour exposure toxicity study (EU 2016).

3.2.2 Terrestrial Effects Analysis

This section of the ecological effects analysis summarizes available brodifacoum terrestrial 

toxicity data for mammals, birds, reptiles, and amphibians. This section also summarizes available 

effects data for terrestrial invertebrates and plants. There are several acute toxicity data values 

for various species in review documents that cite older studies. These review documents are cited 

with the reported values to demonstrate the range of sensitivities between species.

3.2.2.1 Mammals

Brodifacoum is considered very highly acutely toxic to mammals in oral exposures. Oral toxicity 

values range from 0.42 mg/kg-bw for the rat to greater than 25 mg/kg-bw for sheep (Table 4).

Acute dermal and inhalation toxicity is also high for mammals (Table 2). Sublethal effects include 

hemorrhaging, weight loss, decreased activity levels, loss of equilibrium, and lethargy (USEPA 

2020b)

Table 4. Brodifacoum acute oral and dietary toxicity to mammals.

Test species Scientific Name Test Reference

Rat Rattus norvegicus LD50 Acute oral: 0.42 mg/kg-bw (USEPA 2004;2020b)

Rat Rattus norvegicus LC50 Acute dietary: 0.55 mg/kg-diet (USEPA 2004;2020b)
19

Meadow vole Microtus sp. LC50 Acute dietary: 1.4 mg/kg-diet (USEPA 2020b;2024a)

Mink Mustela sp. LD50 Acute oral: 9.2 mg/kg-bw (USEPA 2004)

Cat Felis catus LD50 Acute oral: ~25 mg/kg bw (USEPA 2004)

Sheep Ovis aries LD50 Acute oral: >25 mg/kg-bw (USEPA 2004)

Short- and long-term exposure to brodifacoum results in various sublethal effects that are 

summarized in Sections 2.3.3 through 2.3.8 of this risk assessment.

3.2.2.2 Birds

Brodifacoum is very highly toxic to birds. The lowest reported acute oral LD50 for birds is 0.26 

mg/kg-bw for the mallard (Anas platyrhynchos), and the lowest reported subacute median lethality 

dietary concentration (LC50) is 0.8 mg/kg-diet for the bobwhite (Colinus virginianus) (USEPA 

2020b) (Table 5). Birds exposed to sublethal concentrations exhibit various symptoms such as 

hemorrhaging, weight loss, decreased activity levels, wing droop, loss of equilibrium, lethargy,

and other sublethal effects. No chronic or reproductive avian studies are available for 

brodifacoum.

Table 5. Brodifacoum toxicity to birds.

Test species Scientific Name Test Reference

Mallard Anas platyrhynchos LD50 Acute oral: 0.26 mg/kg-bw (USEPA 2020b)

Mallard Anas platyrhynchos LC50 Subacute dietary: 2.7 mg/kg-diet (USEPA 2020b)

Japanese Quail Coturnix japonica LD50 Acute oral: 11.6 mg/kg-bw (USEPA 2024a)

Bobwhite Colinus virginianus LC50 Subacute dietary: 0.80 mg/kg-diet (USEPA 2020b)

Ring-necked 

Pheasant

Phasianus colchicus LD50 Acute oral: 0.545 mg/kg-bw USEPA 1992 as 

cited in (USEPA 

2024a)

3.2.2.3 Reptiles and Amphibians (terrestrial phase)

The limited data on brodifacoum effects on turtles shows low toxicity. Mauldin et al. (2020)

administered brodifacoum by oral gavage to painted wood turtles (Rhinoclemmys pulcherrima) 

twice over a seven-day period and monitored for acute and sublethal impacts for 14 days. Wood 

turtles administered the low concentration (160 μg/mL; range 0.0914–0.119 mg/kg-bw) and high 

concentration (1,605 μg/mL; 0.888–1.131 mg/kg-bw) brodifacoum solutions did not exhibit acute 

lethal or sublethal effects. Both gavage solution concentrations exceeded the solubility limit for 

brodifacoum in water and would not occur in water bodies. 

In another study, painted wood turtles were fed even higher brodifacoum doses (1.6 mg/kg-diet). 

No turtles died or showed signs of ill health prior to being euthanized one week later. The turtle 

with the highest liver residue level (2.02 parts per million (ppm)) weighed 0.7 lb. (319 g), indicating

it received about 500 ppm (0.5 mg) of brodifacoum, which is the equivalent of 20 pellets of

Brodifacoum-25D Conservation (0.0025% w/w (25 ppm)) (USFWS 2011).

Weir et al. (2016) reported an LD50 value of greater than 1,750 mg/kg-bw in a 14-day study using 

the western fence lizard (Sceloporus occidentalis). This study demonstrated lower toxicity of 

brodifacoum to lizards when compared to mammals and birds. 

Mauldin et al. (2020) dosed green iguanas (Iguana iguana), giant ameivas, or South American 

ground lizard, (Ameiva ameiva) and boa constrictors (Boa constrictor) twice over a seven-day 

period and monitored for acute and sublethal impacts for 14 days. Three ameivas died in the low 

dose brodifacoum treatment level (0.134–0.183 mg/kg-bw) and one in the high dose (1.339–1.781 

mg/kg-bw). One iguana in the low brodifacoum treatment level died (0.242–0.321 mg/kg-bw); 
20

however, no mortality was observed in the high brodifacoum dose level (2.293–3.178 mg/kg-bw). 

Iguanas at low and high doses following treatment showed markedly dark coloration that is 

frequently considered a sign of stress. There was no change in coloration noted in the control 

animals. Several treated ameivas were notably lethargic or unresponsive following dosing, which 

was not observed in the controls. No mortalities or behavioral effects were noted in low or high 

doses administered to boa constrictors.

3.2.2.4 Terrestrial Invertebrates and Microorganisms

Effects data are limited for terrestrial invertebrates, but earthworm, snail, and crab exposures 

show low toxicity after exposure to high concentrations of a brodifacoum formulation in laboratory 

toxicity testing (Booth et al. 2003). USEPA (2020b) reports the results from an earthworm study 

where the Eisenia foetida 14-day LC50 (mg/kg-soil) was greater than 994 mg/kg-soil, suggesting 

low toxicity. Pain et al. (2000) also demonstrated low brodifacoum toxicity to the hare-lipped land 

crab (Johngarthia (formerly Gecarcinus) lagostoma). However, on Palmyra Atoll, some fiddler 

crabs (Uca tetragonon) may have died from brodifacoum poisoning in conjunction with the rat 

eradication (Pitt et al. 2015). USEPA (2020b) pesticide incident reporting suggests a low number 

of crab mortalities associated with SGAR use. 

3.2.2.5 Terrestrial Plants

No toxicity data appears to be available testing the effects of brodifacoum on terrestrial plants.

Acute and chronic adverse effects on terrestrial plants are not anticipated based on the mode of 

action of brodifacoum, low bioavailability in soil, and a lack of a similar pathway in plants.

4 EXPOSURE ASSESSMENT

4.1 Human Health Exposure Assessment

WS uses Brodifacoum-25W Conservation and Brodifacoum-25D Conservation to assist other 

Federal agencies and U.S. Territories with rat and mouse eradication for island conservation

purposes. These pelleted formulations are restricted use pesticides, thus only certified applicators 

or persons under their direct supervision who are employees or under direct supervision of federal 

agencies responsible for wildlife management may use the product. WS also uses limited 

amounts of Talon Weatherblok XT, a paraffin wax block formulation, to control Norway rats and 

house mice. The Weatherblok label requires the use of tamper-resistant bait stations in residential 

structures, USDA-inspected facilities, and treatment locations accessible to children, pets, and 

nontarget mammals and birds. For all above ground outdoor applications, bait stations are 

required. In addition, the Weatherblok label only allows applications in and within 100 feet of 

manmade structures.

Exposure assessments estimate the potential exposure of humans to brodifacoum. An identified 

exposure pathway for brodifacoum includes (1) a release from a source, (2) an exposure point 

where contact can occur, and (3) an exposure route such as ingestion, inhalation, or dermal 

contact (USEPA 1989). Exposures for the identified human populations are qualitatively evaluated 

for each identified exposure pathway.

4.1.1 Identification of Potentially Exposed Human Populations and Complete Exposure 

Pathways

Based on the expected WS use pattern and label restrictions for brodifacoum applications, 

workers applying brodifacoum in the field are the most likely subgroup of the human population 

to be exposed to brodifacoum. Exposure during transportation is not anticipated because the 

material is sealed. Brodifacoum formulations are ready to use with no mixing required. The label 

application methods include tamper-resistant bait stations, burrow baiting, canopy baiting with 
21

bait sachets, and aerial and ground broadcast baiting, with broadcast baiting having the greatest 

potential for human exposure. Supplemental labels may allow additional hand spot baiting 

application methods on an island-by-island basis. For example, the current Brodifacoum-25D 

Conservation and Brodifacoum-25W Conservation supplemental labels for use on Wake Atoll and 

Midway Atoll National Wildlife Refuge list the use of bait trays, and the current Brodifacoum-25W 

Conservation supplemental label for Wake Atoll allows the use of elevated and floating bait 

stations.

The current labels for Brodifacoum-25D Conservation and Brodifacoum-25W Conservation 

Section 3 labels do not allow broadcast applications in areas of human habitation or over human 

residences. Ground or aerial broadcast applications of brodifacoum formulations is prohibited by 

the label in areas of human habitation unless allowed by USEPA for specific island projects under 

supplemental labels (USEPA 2019a;b;2021;2022b). When a conservation project does occur on 

an island with a permanent residential community, such as in the case of Wake Atoll and Midway 

Atoll National Wildlife Refuge, additional protection measures requirements may be implemented

as part of the supplemental label or in project planning. For example, the below mitigation 

measures will be used to protect human health from brodifacoum applications that are planned

for rodent eradication at Wake Atoll:

• Residents will be informed of the project activities, including rodenticide use and risks, 

the planned application methods, potential pathways of the toxins, and requirements for 

reporting incidents during and after the application process that might have deviated 

from the application plan (e.g., bait spillage).

• Pre- and post-test water sources and marine food sources to determine any risks to 

staff.

• Post warning signs before, during, and after a bait application.

• Medical staff will be equipped and trained (as needed) to assess prothrombin and other 

potential indices of anticoagulant poisoning.

• Cover wells and water tanks during aerial broadcast applications. Alternately, hand 

broadcast applications, bait stations, bait trays, and bait sachets can be used around 

wells and water tanks.

• Recommend a three-month consumption prohibition for fish caught in the lagoon.

• Incinerate recovered rat carcasses, where feasible.

Implementation of the above mitigation measures in areas of human habitation for future 

brodifacoum island conservation uses will be site specific and may include other measures where 

appropriate. Any of these measures would be part of a supplemental label for such uses where 

there is a proposal to broadcast apply brodifacoum in areas of human habitation.

The potential for exposure from the proposed WS use pattern is low, however accidental exposure 

may occur during application. The risk of exposure via ingestion or inhalation is minimal due to 

outdoor use and label application restrictions and PPE.

A significant direct exposure pathway to the Brodifacoum-25D Conservation and Brodifacoum25W Conservation formulations used by WS is not identified for the public because this product 

is a restricted use pesticide and can only be sold to certified applicators that are employees of 

federal agencies responsible for wildlife management for conservation uses on islands. The 

brodifacoum formulations can only be applied by a certified applicator or persons under their direct 

supervision. Belowground burrow baiting is only permitted in uninhabited non-crop areas. Bait 

sachets may be used within and around institutional structures, within and around uninhabited 

man-made structures, around the perimeter of hydroponic gardens or greenhouses, freshwater 
22

tanks, seeps, pools, and ponds, and all other non-crop areas on islands, including canopies of 

trees and shrubs and subterranean spaces. Enclosed bait stations may be used within and around 

any man-made structure, within and around non-operational ventilation ducts, around the 

perimeter of freshwater tanks, seeps, pools, and pods, and all other non-crop areas on islands. 

Similarly, a significant direct exposure pathway to Talon Weatherblox XT formulation used in by

WS is not identified for the public due to the label’s application restrictions and WS use patterns.

As a result of these use restrictions for brodifacoum formulations used by WS, the public is not 

considered a vulnerable population for direct exposure to brodifacoum used by WS.

Although oral exposure to all formulations of brodifacoum is acutely hazardous, label restrictions 

render accidental dietary exposure an incomplete exposure pathway. Brodifacoum is a non-food 

use chemical with no anticipated drinking water exposures based on label restrictions.

Brodifacoum is immobile in soil, and mobility into nearby water bodies or aquifers is not expected. 

In addition, label restrictions state that no applications are allowed directly to water, areas where 

surface water is present, or intertidal areas below the mean high-water mark (except for elevated 

and floating bait stations used in island conservation) (USEPA 2019a;b;2021;2022b). Placement 

of elevated and floating bait stations is allowed in intertidal zones above the mean low tide mark 

and below the mean high tide water mark on the current supplemental label for Wake Atoll. In 

addition to these restrictions, floating bait stations may only be used where the water is calm 

enough that the bait stations will not be inundated with water or capsize; the stations must be 

tethered or attached to a stationary object. The supplemental label requires floating bait stations 

in intertidal zones be removed if stormy weather is forecasted. 

Brodifacoum has a low potential for volatilization due to its low vapor pressure. As a result of 

these label restrictions and brodifacoum’s environmental fate properties, surface and 

groundwater exposure pathways are also incomplete. 

4.1.2 Occupational Exposure Evaluation

This section qualitatively evaluates worker exposures from a direct contact pathway while 

applying baits. USEPA (2020a) finds that “for loose formulations, occupational dermal and 

inhalation exposures are anticipated for handlers (e.g., application by hand, handheld, 

ground/aerial equipment).” Brodifacoum’s chemical properties (molecular weight of 523.4 g/mol 

and log Kow of 8.5) indicate a low potential for dermal adsorption (USEPA 2016a).

Following label directions, including the use of PPE, will minimize worker exposure to brodifacoum 

via inhalation and dermal contact routes. Proper PPE for applicators, other handlers, and anyone 

who retrieves carcasses or unused bait of Brodifacoum-25D Conservation and Brodifacoum-25W 

Conservation formulations include long pants, shoes plus socks, and barrier laminate gloves. 

Applicators performing aerial applications Brodifacoum-25D Conservation and Brodifacoum-25W 

Conservation formulations, and persons retrieving unused bait following aerial applications must 

additionally wear protective eyewear or face shield and a minimum of a NIOSH-approved 

respirator (specifics provided on the labels). Proper PPE for applicators, other handlers, and 

anyone retrieving carcasses or unused bait for Talon Weatherblok are similar, however require 

the use of waterproof gloves in place of barrier laminate gloves (USEPA 2019a;b;2021;2022b). 

WS may monitor treatment sites for impacts to target and non-target species. Personnel that 

conduct posttreatment monitoring follow applicable standard operating procedures and pesticide 

labels that include appropriate PPE for posttreatment activities. Before monitoring, WS train 

personnel in the proper handling of animals and use of PPE. Monitoring does not occur during 
23

treatment so exposure to brodifacoum during treatment would not occur. Personnel wear PPE 

when handling live animals and animal carcasses and when handling bait pellets in the 

environment. Based on these safeguards, monitoring activities are unlikely to pose health and 

safety concerns for personnel or the public.

4.2 Ecological Exposure Assessment

This section provides a qualitative assessment of the exposure of nontarget terrestrial and aquatic 

organisms from brodifacoum applications. 

The application method will affect nontarget species' primary and secondary exposure potential. 

Depending on the formulation used for treatment, the label may allow for applications 

belowground by hand, bait bolas, in tamper-resistant bait stations, or through aerial and ground 

broadcast applications. 

4.2.1 Aquatic Exposure Assessment

The labels for brodifacoum formulations do not allow applications to water bodies. Island 

conservation applications of brodifacoum are made in a manner that will reduce the likelihood of 

pesticide deposition into aquatic areas such as interior waterbodies and the outer coastline of 

islands. The following additional restriction statements are examples of mitigation measures that 

have been implemented in previous island conservation applications to reduce the likelihood of 

aquatic exposure: 

• No broadcast bait applications over uncovered, inland waterbodies.

• No rodenticide applications below the mean high tide water line except for floating and 

elevated bait stations, which can be placed between the mean low tide and mean high 

tide water lines in areas with no predictable wave action.

• No broadcast applications within 3.3 ft (1 m) of the water’s edge for uncovered, inland, 

freshwater bodies.

• Use of a deflector shield (helicopter), directional spreader (Uncrewed Aerial Vehicle 

(UAV)), or narrow swath bucket (helicopter or UAV) for aerial broadcast applications 

adjacent to waterbodies or along the coastal shoreline.

• Use of hand broadcast or narrow baiting by helicopter or UAVs for aerial broadcast for 

applications adjacent to waterbodies, where feasible.

• Limit aerial and most ground broadcast applications to the dry season, reducing offsite 

runoff to waterbodies.

• Restrict aerial broadcast applications to when wind speeds are below 35 mph, reducing 

the likelihood of off-site deposition of pellets.

• Cover wells and water tanks during aerial broadcast applications.

• Hand broadcast applications, bait stations, bait trays, and bait sachets can be used 

adjacent to wells and water tanks.

The above mitigation measures in addition to other label restrictions for brodifacoum formulations 

are designed to reduce the probability of brodifacoum transport to aquatic areas from drift and 

runoff. Incidental deposition of brodifacoum into water resources may occur through drift or runoff 

from broadcast applications; however, the expected levels in waterbodies and the surrounding 

ocean would be negligible (Fisher et al. 2010).

Any brodifacoum that would enter the water will do so as a pellet or block that would become 

saturated and sink to the bottom sediment where it would rapidly degrade. Pellet baits have been 

shown to degrade in water within minutes to less than five hours in previous eradication efforts

(Empson and Miskelly 1999, Howald et al. 2009, Samaniego-Herrera et al. 2014). Additionally, 

any pellets that are discharged into the ocean side of an island would degrade even more rapidly 
24

through the mechanical forces of wave action. 

Direct exposure to fish that may consume pellets that incidentally enter aquatic systems appears 

to be species dependent. Howald et al. (2009) also reported that bait pellets were not consumed 

by fish or aquatic invertebrates after rodenticide applications on Anacapa Island. However, other 

studies have shown that fish will consume bait pellets. USFWS (2019) reported that bait material 

or a pyranine biomarker were observed in specimens of pinktail triggerfish (Melichthys vidua), 

black triggerfish, stocky hawkfish (Cirrhitus pinnulatus), and blue-lined snapper (Lutjanus 

kasmira) immediately after brodifacoum applications. No evidence of bait consumption was found 

in blacktail snapper or blotcheye soldierfish (Myripristis berndti). Empson and Miskelly (1999)

reported that three species of fish were seen eating non-toxic bait within 15 minutes of entering 

the marine environment in a rodent eradication project on Kapiti Island. Bait consumption by 

marine fish would be short-term due to the rapid degradation of pellets once they enter water.

Brodifacoum has low water solubility, 0.24 mg/L at a pH of 7.4, and environmental fate properties 

that suggest that residues in water would bind to suspended solids and sediment. Its low solubility 

and high binding affinity for soil also reduce the likelihood of leaching into groundwater resources.

The environmental fate properties of brodifacoum will reduce the probability of exposure to 

vertebrates and invertebrates that occupy the water column. Aquatic exposures would be greatest 

for aquatic biota that occupy the sediment or would consume benthic prey items.

Secondary exposure to brodifacoum may occur for marine fish species that feed near shore. 

Masuda et al. (2015) evaluated 11 previous accounts of residue examination of coastal marine 

species following aerial applications of brodifacoum bait and found the overall rate of residue 

detection was 3.1% for fish (2 of 65 samples tested) and 5.6% for marine invertebrates (11 of 196 

samples tested). The risk to marine fish from secondary exposure to brodifacoum is low based 

on the low frequency of detection in potential prey items. The exposure to marine fish from 

secondary exposure will decrease over time as brodifacoum is metabolized and degraded in the 

marine environment.

4.2.2 Terrestrial Exposure Assessment

Brodifacoum residues in terrestrial wildlife can occur from primary and secondary oral exposures.

Terrestrial invertebrates and vertebrates may be directly exposed to brodifacoum from consuming 

the bait pellets or ingestion of soil and water that contains brodifacoum residues. Secondary 

exposure will occur when nontarget terrestrial vertebrates consume invertebrate and vertebrate 

prey items that contain residues of brodifacoum. These exposures can be both short- and longterm. A majority of the WS use of brodifacoum is for island conservation eradication projects. 

Compared to other registered uses of brodifacoum, the use pattern is shorter in duration since 

the eradication project is set for a specific time interval when making broadcast applications over 

large areas. There may be some post-eradication treatment exposure due to a need to mop up 

any remaining rodents that were not eradicated during the primary eradication effort. These 

applications are typically much smaller in scale and directed when compared to the primary 

application. Inhalation and dermal exposure to brodifacoum are not anticipated to be a significant 

exposure pathway for nontarget wildlife. The use of a bait pellet in the APHIS brodifacoum

formulations and bait block in the Talon Weatherblok XT formulation and the low potential for 

brodifacoum to volatilize suggests a low potential for inhalation and dermal exposures. 

Primary Exposure

Primary or direct exposure will be greatest for nontarget animals that consume the bait. Dyes 

have been added to some brodifacoum bait formulations to reduce primary exposure to nontarget 

birds. Blue and green dyes added to pellets have been shown to deter or reduce bird 
25

consumption, reducing the risk of rodenticide exposure (Marples et al. 1998, Hartley et al. 1999, 

Hartley et al. 2000, Weser and Ross 2013). For bait that are attractive to nontarget animals, the

duration of direct exposure will depend on how long bait is available for consumption. In some 

cases, baits not removed by the target rodent species and any nontarget species will be 

recovered, but this will vary based on the feasibility of collecting unrecovered baits. Any 

unrecoverable baits left in the environment from WS use will slowly degrade. Brodifacoum has a 

half-life of 157 days in sandy clay loam soil incubated in the dark at 21°C (USEPA 1998). It is 

stable to hydrolysis (USEPA 1998). On Little Barrier Island in New Zealand, brodifacoum bait 

pellets in exclusion cages were nearly completely disintegrated by day 100 after application 

(Fisher et al. 2010). About 96% of aerially applied brodifacoum pellets had completely broken 

down by 120 days in open grassed areas; degradation in the forested area was slightly slower 

(Fisher et al. 2010).

Secondary Exposure

Secondary exposure of brodifacoum to scavenging and predatory birds and mammals have been 

noted for various species. There is the potential for brodifacoum residues to occur in terrestrial 

invertebrates that consume brodifacoum pellets or blocks and then be exposed to birds and 

mammals that consume invertebrates (Howald et al. 2009). Walther et al. (2021) noted 

brodifacoum residues in three insectivorous bird species that frequent farms where brodifacoum 

use was reported. Within the sampled birds, the Great tit, Paruys major, European robin, 

Erithacus rubecula, and Dunnock, Prunella modularis, had brodifacoum liver tissue residues of

23.3, 44.4, and 40.9%, respectively. Residue levels and frequency decreased the further the 

collection distance from fields where brodifacoum had been used.

Herring et al. (2022) reported brodifacoum exposure in the turkey vulture and the federally listed 

California condor. In the turkey vulture, 80% of plasma samples showed detectable levels of 

brodifacoum, while in the California condor, 56% of liver samples showed detectable levels of 

brodifacoum. Niedringhaus et al. (2021) reported that anticoagulant rodenticide exposure in bald 

eagles (Haliaeetus leucocephalus) and golden eagles (Aquila chrysaetos) was 83% and 77%,

respectively, when measuring residues in the liver. Brodifacoum was the most frequently detected 

anticoagulant rodenticide at 81%. Brodifacoum secondary exposure has also been observed in 

other predatory and scavenging bird species, such as owls (Wiens et al. 2019, Hofstadter et al. 

2021) and hawks (Murray 2017;2020, Hopf-Dennis et al. 2022), and in one passerine species,

the Stewart Island robin (Petroica australis rakiura) (Masuda et al. 2014). The secondary 

exposure noted in the passerine species is from nestlings consuming invertebrate prey that the 

adults bring to the nestlings.

Musto et al. (2024) reported that 61.8% of samples collected from grey wolves (Canis lupus) had 

detectable levels of anticoagulant rodenticides with brodifacoum being the most common. 

Secondary mammal exposure to brodifacoum has also been noted in the Eurasian river otter, 

Lutra lutra. Regnery et al. (2024) reported liver brodifacoum residues ranging from 11% to 81.1% 

in Eurasian river otters sampled from various German federal states. Otters are piscivorous 

predators with secondary exposure from consuming contaminated fish prey. Murphy et al. (1998)

reported a 78%, 71%, and 56% incidence of brodifacoum residues in the livers of stoats (Mustela 

erminea), weasels (M. nivalis), and ferrets (M. furo), respectively, after a large-scale eradication 

of invasive rats and opossums in a New Zealand forest habitat.

Brodifacoum has also been observed in reptiles, specifically snake and lizard species. Lettoof et 

al. (2020) reported brodifacoum residues in the livers of a rodent predator snake species, a frog 

predator snake species, and an omnivorous lizard. Sample sizes were low, however brodifacoum 

was the most detected anticoagulant rodenticide.
26

Primary and secondary exposure to any terrestrial vertebrate is of concern. Brodifacoum 

exposure to birds is of particular concern as islands serve as breeding and overwintering sites for 

many seabirds and shorebirds. WS working with its cooperators on island conservation projects 

have implemented several mitigation measures to reduce disturbance and exposure to birds from 

brodifacoum applications for island conservation projects. Below is a list of measures that may be 

used to reduce disturbance and minimize primary and secondary brodifacoum exposures to birds 

and mammals:

• Select the color and size of the rodenticide baits to minimize attractiveness of the bait to 

birds.

• Use UAVs in areas of high bird activity to reduce disturbance and the probability of bird 

strikes.

• Remove animal carcasses that could potentially be a source of secondary poisoning for 

analysis or incineration.

• Use special measures, such as hand broadcast applications or the use of deflector 

shield, directional spreader, or trickle bucket for aerial applications, to prevent bait from 

entering the water and contaminating food sources that are bird and mammal prey 

items. 

• Conduct broadcast applications when seasonal bird activities, including nesting, are 

minimal.

The use of the above mitigation measures to reduce brodifacoum exposure to birds and mammals

is site specific. For example, the removal of carcasses may not be feasible if they are in unsafe 

or inaccessible areas, or collecting the large numbers of dead rodents may be impractical.

5 RISK CHARACTERIZATION

This section discusses the qualitative risks associated with the proposed use of brodifacoum. The 

evaluation of documented brodifacoum health exposure data and relevant animal exposure 

studies applied to exposure assumption scenarios can quantify the risk of impact to human health 

and nontarget fish and wildlife if accidentally exposed. Deterministic methods are used, where 

appropriate, to determine if expected environmental residues exceed toxicity data suggesting 

possible risk. In other cases, a qualitative discussion regarding risk may rely on literature and 

additional information to further elaborate on the potential for injury or harm.

5.1 Human Health 

Risks associated with adverse human health are characterized qualitatively for this section. 

Occupational risk for applicators was not quantified due to the lack of a relevant toxicity endpoint

to estimate a hazard quotient (HQ). Dermal and inhalation exposures were identified as a potential 

exposure pathway; however, sublethal and/or long-term inhalation and dermal toxicity data was 

not available for either pathway. Sublethal and chronic toxicity data is available for oral exposures;

however, this exposure pathway is not relevant for estimating inhalation and dermal risks to 

applicators.

Occupational risks for applicators are anticipated to be low due to the lack of dietary exposure 

and label requirements regarding PPE when loading, applying, or handling products containing 

brodifacoum. PPE requirements will minimize inhalation and dermal risks to applicators. 

Brodifacoum risks to the public from island conservation uses are low. To date no adverse effects 

to human health have been reported when using brodifacoum as a rodenticide in island 
27

conservation projects. Castaño et al. (2023) reviewed data from 153 island rodent eradication 

projects, many of which used brodifacoum as the primary rodenticide. There were no reports of 

adverse effects to the public or workers from oral, dermal, or inhalation exposures, or secondary 

or tertiary exposures. 

The low risk to the public is due to the label restrictions and additional mitigation measures (see 

Section 4.1.1) including those on the supplemental labels which have higher broadcast use rates

(USEPA 2019a;b). For many sites that have been treated in past eradication efforts the public is 

not allowed on the island or there is no permanent habitation. In situations where the public may 

be present, the label restrictions and other mitigation measures reduce the risk to the public. 

Finally, brodifacoum is not registered for use on food crops, and other dietary resources such as 

drinking water are at low risk from contamination due to label restrictions, additional mitigation 

measures (see Section 4.2.1), and its environmental fate. Similarly, the risk to the public from WS 

use of Talon Weatherblok XT is low due to label restrictions and WS use patterns.

5.2 Ecological Risks

Risk characterization combines information from the dose-response assessment with the 

exposure assessment to determine the potential adverse effects on aquatic and terrestrial 

species. In this risk assessment, WS uses USEPA’s risk evaluations (USEPA 2016c;2020b), 

peer-reviewed scientific literature, product labels, and WS use patterns to characterize the risks 

associated with WS applications of brodifacoum bait. 

5.2.1 Aquatic

Acute and chronic risks to aquatic vertebrates and invertebrates are anticipated to be low for most 

brodifacoum uses. Aerial broadcast applications pose the greatest risk to nontarget aquatic 

organisms; however, as discussed in section 4.2.1, WS uses additional measures to reduce the 

likelihood of brodifacoum residues entering waterbodies and the surrounding marine 

environment. Nontarget aquatic risk would be greatest for small, isolated waterbodies occurring 

on an island. Shallow lagoon areas on the perimeter of the island could also pose a risk to aquatic 

organisms; however, tidal effects, brodifacoum’s environmental fate, and dilution will reduce the 

risks. 

Furthermore, any brodifacoum-containing rodenticide pellets or blocks that enter the marine 

environment will become saturated and break down rapidly, with remaining brodifacoum residues 

being diluted and partitioning to suspended solids and sediment, where the brodifacoum will 

slowly degrade, resulting in low risk to marine invertebrates. USFWS (2019) reported no impacts 

to coral species associated with the rat eradication project on Palmyra Atoll. Caliani et al. (2023)

sampled several fish species 10 days after a rodent eradication project on Tavolara Island, an 

Italian Marine Protected Area. Results from the study showed no brodifacoum residues in fish 

and no effect on various biomarkers suggesting no sublethal impacts.

Brodifacoum concentrations at which adverse effects have been reported would not occur under 

any realistic exposure scenario using typical use patterns. For example, if one pound of bait were 

dissolved into a 10’x10’x1’ or any 100 ft2 area of ocean, it would result in about 0.004 mg/L in that 

area (this is not likely to happen as discussed because it is more likely to bind to sediment and 

soil). This resulting concentration is insufficient to result in adverse effects to aquatic organisms

based on available toxicity data. Anticipated brodifacoum risks to the marine environment will be 

very low based on label requirements for treatment and additional mitigation measures used by 

WS to protect marine environments.
28

Howald et al. (2009) also reported that bait pellets were not consumed by fish or aquatic 

invertebrates after rodenticide applications on Anacapa Island. However, other studies have 

shown that fish will consume bait pellets. USFWS (2019) reported that bait material or a pyranine 

biomarker were observed in specimens of pinktail triggerfish (Melichthys vidua), black triggerfish, 

stocky hawkfish (Cirrhitus pinnulatus), and blue-lined snapper (Lutjanus kasmira) immediately 

after brodifacoum applications. No evidence of bait consumption was found in blacktail snapper 

or blotcheye soldierfish (Myripristis berndti). Empson and Miskelly (1999) reported that three 

species of fish were seen eating non-toxic bait within 15 minutes of entering the marine 

environment in a rodent eradication project on Kapiti Island. Bait consumption by marine fish 

appears to be species dependent and based on the availability of the pellet, which is short-term. 

Brodifacoum-containing pellets that enter the marine environment break down rapidly with 

remaining brodifacoum residues being diluted and partitioning to suspended solids and sediment, 

where brodifacoum will slowly degrade. The amount of brodifacoum that could enter the marine 

environment is expected to be very low from the proposed applications based on the application 

sites and mitigation measures designed to protect aquatic resources. Risks to marine fish species 

from brodifacoum residues in water or sediment is expected to be negligible. 

Brodifacoum residues could potentially accumulate in marine invertebrates and pose a chronic 

risk. Masuda et al. (2015) evaluated eleven previous accounts of residue examination of coastal 

marine species following aerial applications of brodifacoum bait and found the overall rate of 

residue detection was 5.6% for marine invertebrates (11 of 196 samples tested). The sublethal 

and chronic effects from these types of exposures to marine invertebrates is unknown; however, 

the frequency of detection is low, suggesting no population level effects to marine invertebrates.

The low incidence of brodifacoum residues would suggest secondary risks to aquatic organisms 

that consume marine invertebrates would also be low.

The exposure to aquatic invertebrates would be higher for sediment dwelling invertebrates due to 

the chemical and environmental fate characteristics of brodifacoum. Brodifacoum toxicity to 

benthic invertebrates is expected to be comparable based on available freshwater invertebrate 

toxicity data. The risks to benthic invertebrates are likely low due to the reduced bioavailability 

that may occur as brodifacoum binds tightly to soil and sediment (USEPA 2020b). Any impacts to 

sediment-dwelling invertebrates would be short- or long-term due to the persistence of 

brodifacoum. 

Marine mammals, sea turtles, and offshore fish species are anticipated to have negligible risk of 

adverse impacts from any incidental brodifacoum transport to sea water. Dilution, the physical 

wave action to break up pellets, and the environmental fate of brodifacoum would not result in 

detectable levels of brodifacoum where those species would be expected to forage.

Based on the lack of aquatic exposure, label restrictions, and WS use pattern, APHIS considers 

the risk to aquatic species as negligible for island conservation uses. Brodifacoum risks to aquatic 

nontarget species would be even less under non-island conservation uses. Non-island 

conservation uses are restricted to near structure applications with lower use rates and more 

restrictive application methods than those used for island conservation. Additionally, WS 

personnel use is negligible for non-island applications.

5.2.2 Terrestrial

Brodifacoum toxicity and exposure can result in acute and chronic primary and secondary risks 

to most terrestrial vertebrates. Direct ingestion of bait by nontarget terrestrial wildlife would be 

expected to result in adverse acute and chronic effects dependent on the dose received and 

duration of exposure.
29

USEPA (2020b) conducted a screening level risk assessment to evaluate the direct risk to birds, 

reptiles, and mammals from brodifacoum exposure across multiple body weights and food intake 

values. In the absence of standardized toxicity data for reptiles, USEPA uses bird toxicity data to 

estimate acute risks. The exposure estimates were divided by acute toxicity values that were

adjusted for body weights to calculate a risk quotient (RQ) (Table 6). USEPA uses levels of 

concern (LOC) to determine if there is a risk to a group of animals by comparing the RQ to the 

LOC. In the case of terrestrial vertebrate wildlife USEPA uses a LOC of 0.5. An RQ above 0.5 

suggests an acute high risk to nontarget vertebrates. USEPA also uses an LOC of 0.1 for 

determining risk to federally threatened and endangered species. A RQ was estimated for 

different body weight categories of birds and mammals (Table 6).

Table 6. Estimated acute risk quotient (RQ) values for brodifacoum (25 ai-mg/kg bait) in birds and 

mammals.

Class Weight 

(g)

Adjusted LD50

(mg ai/kg-bw1)

Brodifacoum

intake2

(mg ai/kg-bw)

RQ3 Brodifacoum

body burden4

(mg ai/kg-bw)

RQ3

Passeriform Birds 20 185.9 6.35 0.03 76 117

Passeriform Birds 100 236.6 4.99 0.02 60 135

Passeriform Birds 1000 334.2 3.53 0.01 42 166

Rodent Mammals 15 5.5 4.77 0.87 57 59

Rodent Mammals 35 4.4 3.29 0.75 39 51

Rodent Mammals 1000 1.9 0.76 0.40 9 27

1 mg ai/kg-bw = milligrams active ingredient per kilogram body weight 

2 Single day of bait exposure

3 Risk quotients in bold exceed the acute high-risk LOC of 0.5.

4 Six consecutive days of bait exposure

Reference: (USEPA 2020b)

The acute high-risk LOC was exceeded for 15g and 35g body weights for mammals in single- and 

six-day exposures. The acute high-risk LOC was not exceeded for any of the three avian body 

weights from a single day exposure, however all LOCs were exceeded when assuming six 

consecutive days of bait exposure. These estimates are screening values that allow risk 

assessors to identify taxa groups requiring additional risk evaluation. The endpoint used to derive 

the effect value is an LD50 which is based on mortality. Sublethal impacts may also occur at lower 

doses and those risks are not estimated in Table 6. These risks will be reduced as the bait is

removed by the target pest and nontarget species, and as the bait pellet and brodifacoum degrade 

in the environment.

Primary and secondary risks of brodifacoum to nontarget mammals and birds will vary based on 

their food preferences. USFWS evaluated the primary and secondary acute risk to seabirds and 

shorebirds on Sand Island at Midway Atoll from Brodifacoum-25W Conservation applications 

(USFWS 2019) (Table 7). USFWS estimated the acute poisoning risk to seabirds and shorebirds 

using acute lethality data and estimating food intake values. Estimates of acute risk from direct 

ingestion of pellets or ingesting prey containing brodifacoum were made by estimating the 

percentage of daily food needed to receive a lethal dose of brodifacoum. USFWS categorized the 

primary and secondary poisoning risk from brodifacoum exposure using toxicity estimates and 

feeding habits for seabirds and shorebirds.

Generally, primary and secondary risks of brodifacoum exposure to seabirds is lower due to their 

feeding habits that consists mostly of marine prey items. For example, the sooty tern, a common 

nesting seabird, has a low risk of primary and secondary exposure to brodifacoum based on their 

diet. Sztukowski and Kelser (2012) demonstrated that sooty tern chicks on Wake Atoll did not 
30

preferentially consume placebo bait pellets, also suggesting a low risk of brodifacoum risk to sooty 

tern chicks. 

Secondary poisoning risks to birds are short- and long-term; however, brodifacoum residues in 

bird prey items such as invertebrates, lizards, and marine fish will decline over time. Wegmann et 

al. (2019) reported no brodifacoum residues in mullet (Moolgarda engeli), cockroaches 

(Periplaneta sp.), geckos (Lepidodactylus lugubris), hermit crabs (Coenobita perlatus), and fiddler 

crabs (U. tetragonon) three years post-eradication on Palmyra Atoll. Siers et al. (2020) reported 

no brodifacoum residues in fish samples collected within the lagoon at Wake Atoll, or within nearshore waters outside the lagoon three years after the 2012 eradication. Traces of brodifacoum 

were detected in 2 out of 20 blacktail snapper (Lutjanus fulvus) fish samples that were collected 

in an intermittent land-locked pond in an area that received significant brodifacoum baiting. 

Although at levels too low to quantify, the study demonstrated that brodifacoum can persist in 

aquatic environments, especially smaller isolated water bodies. 

Table 7. Risk summary for seabirds and shorebirds exposed to brodifacoum from rat eradication 

activities*.

Species Primary Poisoning Risk Secondary Poisoning Risk

Laysan Albatross, Phoebastria immutabilis

(adult)

Low Low

Black-footed Albatross, P. nigripes Low Low

Albatross (chicks all spp.) Low Low

Wedge-tailed shearwater, Ardenna pacifica Low Low

Christmas shearwater, Puffinus nativitatis Low Low

Great frigatebird, Fregata minor Low Medium

White-tailed tropicbird, Phaethon lepturus Low Low

Red-tailed tropicbird, P. rubricauda Low Low

Masked booby, Sula dactylatra Low Low

Brown booby, S. leucogaster Low Low

Red-footed booby, S. sula Low Low

Black noddy, Anous minutus Low Low

Brown noddy, A. stolidus Low Low

White tern, Gygis alba Low Medium

Sooty tern, Onychoprion fuscatus Low Low

Gray-backed tern, O. lunatus Low Low

Pacific golden plover, Pluvialis fulva High High

Ruddy turnstone, Arenaria interpres High High

Wandering tattler, Tringa incana High High

Gray-tailed tattler, T. brevipes High High

Sanderling, Calidris alba High High

Dunlin, C. alpina High High

Sharp-tailed sandpiper, C. acuminata High High

Bristle-thighed curlew, Numenius 

tahitiensis

High High

*(USFWS 2019)

Birds that consume bait or prey contaminated with bait are at short- and long-term risk from 

brodifacoum. Short-term primary risk is greatest immediately after treatment and will decline as 
31

bait is removed by the target rodents, some nontarget species, and as the pellets degrade in the 

environment. Aerial broadcast applications pose the greatest risk to nontarget species since they 

are typically broadcast over a larger area. Aerial applications typically occur within an approximate

30-day window with 2 to 3 applications during that time under the current supplemental labels.

The FIFRA Section 3 label for Brodifacoum-25D Conservation and Brodifacoum-25W

Conservation allow only 1 to 2 aerial broadcast applications with a 5 to 7-day interval between 

applications. Mitigation measures for nontarget terrestrial vertebrates that were summarized in 

Section 4.2.2 reduce the potential for short- and long-term primary and secondary risks.

Hand baiting using bait bolas, burrow baiting, floating bait stations, and tamper-proof baiting 

stations can be used over a longer period for eradication and control efforts. These application 

methods can result in a short- and long-term risk; however, these methods of application are 

typically used for smaller areas of treatment compared to aerial broadcast applications. Bait 

removal by the target rodent species will reduce long term primary risks to nontarget animals that

may also consume bait. In some cases, for aerial and ground applications, rodents may be 

collected after application, thus reducing short- and long-term secondary risks to nontarget 

animals. As previously stated, the level of carcass removal will vary depending on site conditions. 

For example, collection and disposal may not be feasible if treatments occur in an area where 

there are high natural mortality rates for nontarget species such as bird breeding areas. Label 

requirements for collection and disposal of spilled bait also reduce primary and secondary risks.

Brodifacoum primary and secondary risks to nontarget wildlife have been noted under past use.

USEPA (2020b) reported that second generation anticoagulant rodenticides (SGARs) resulted in 

adverse incident reports for more than 70 species of birds and 30 species of mammals. 

Brodifacoum was linked to approximately 60% of the SGAR incident reports for birds and 43% of 

the incident reports in mammals. Brodifacoum primary and secondary risks to birds have been 

identified in large scale aerial rodent eradication programs. Ebbert and Burek-Huntington (2010)

reported more than 420 bird carcasses were collected after an eradication program to remove the 

Norway rat from Rat Island, Alaska using Brodifacoum-25W Conservation. Approximately 24 

species of birds were collected with glaucous-winged gulls (Larus glaucescens) and bald eagles 

(Haliaeetus leucocephalus) being the most collected. Of the seventy birds necropsied almost all 

showed signs of brodifacoum exposure, including extensive hemorrhaging. Brodifacoum 

exposure continued at Rat Island for at least nine months after application demonstrating acute 

and chronic risks.

There is a low risk to terrestrial invertebrates that are exposed to brodifacoum pellets and blocks. 

Spurr and Drew (1999) reported that terrestrial invertebrates like crickets, beetles, and ants are 

attracted to cereal baits used in rat eradication programs in New Zealand. Terrestrial invertebrates 

may also scavenge dead rats that have been exposed to brodifacoum. Based on available toxicity 

data, the risk to this group of nontarget species is expected to be low. Effects data are limited for 

terrestrial invertebrates, but earthworm, snail and crab exposures show low toxicity after exposure 

to high concentrations of brodifacoum in laboratory toxicity testing (Booth et al. 2003). Pain et al.

(2000) also demonstrated low brodifacoum toxicity to the hare-lipped land crab (Johngarthia 

(Gecarcinus) lagostoma). However, on Palmyra Atoll, some fiddler crabs (U. tetragonon) may 

have died from brodifacoum poisoning in conjunction with the rat eradication (Pitt et al. 2015). 

Applications on Palmyra Atoll were higher than those that have been used on other island 

conservation projects. USEPA (2020b) pesticide incident reporting suggests a low number of crab 

mortalities associated with SGAR use. Any impacts to terrestrial invertebrate populations would 

be expected to be short duration. Bait pellet removal by the target pest and other nontarget 

species, and brodifacoum degradation would allow invertebrate populations to recover.
32

There is the potential for brodifacoum residues to occur in terrestrial invertebrates that consume 

brodifacoum pellets or blocks (Howald et al. 2009). The sublethal impacts of these residues to 

terrestrial invertebrates is unknown but population increases of crabs and other invertebrate 

populations post-eradication suggest that the impacts are minimal and transient. The presence of 

brodifacoum residues in terrestrial invertebrates does pose a secondary risk for those nontarget 

species that rely on terrestrial invertebrates as a food source.

Brodifacoum binds to soil and is not considered systemic in plants (WHO 1995). However, in a 

recent study dosing soil with brodifacoum at 100 g/m2 or 500 g/m2 resulted in residues in wheat 

ranging from 0.012 mg/kg to 0.0436 mg/kg (Miňo et al. 2019). For the study, bait pellets were 

incorporated into the soil and allowed to degrade releasing brodifacoum into the soil. The removal 

of bait by the target rodent species and other nontarget species suggests that long term exposure 

of plants to brodifacoum in soil is unlikely. The use of a weather-resistant pellet formulations, 

removal of pellets by the target species and other nontarget animals, and the anticoagulant mode 

of action of brodifacoum suggests no direct risks to terrestrial plants. 

APHIS recognizes the primary and secondary risks associated with brodifacoum use in island 

conservation projects. Mitigation measures to reduce terrestrial and aquatic exposure reduce 

these risks but do not eliminate them. Castaño et al. (2021) identified three strategies that can be 

used to reduce nontarget risk from rodenticide use in invasive rodent eradication programs on 

islands. Strategies include exposure avoidance, risk minimization, and remediation with several 

tactics identified within each strategy. Some of these measures are already components of island 

eradication efforts using brodifacoum. The use of other strategies in future island conservation 

projects will be dependent upon site specific conditions.

The use of brodifacoum and other rodenticides as a tool in island conservation has been shown

to provide beneficial impacts to native flora and fauna post eradication (Thibault 1995, Jouventin 

et al. 2003, Harper and Bunbury 2015, Newton et al. 2016, Graham et al. 2018, Wolf et al. 2018, 

Herrera-Giraldo et al. 2019, USFWS 2019). The primary and secondary adverse risks to nontarget 

fish and wildlife from brodifacoum applications can be offset by the positive impacts invasive 

rodent eradication and control can have on endemic island species post eradication. 

Brodifacoum risks to terrestrial nontarget species are considered much lower for non-island 

conservation uses when compared to island uses. Non-island conservation uses are restricted to 

near structure applications (i.e. no applications beyond 100 feet of a structure) with lower use 

rates, no broadcast applications, and more restrictive application methods than those used for 

island conservation purposes. Additionally, WS personnel use is negligible for these types of 

applications.

6 UNCERTAINTIES AND CUMULATIVE IMPACTS

The uncertainties associated with this risk evaluation arise primarily from the limited toxicity 

information available for the various brodifacoum formulations. Unpublished acute toxicology 

studies submitted to USEPA by registrants and individual formulation safety data sheets provide 

limited acute mammalian toxicity values, which are then used to make general conclusions 

concerning the impact of brodifacoum on humans and the non-target environment.

Other uncertainties related to chronic and sublethal effects data for some fish and wildlife and 

surrogacy of test organisms are typical for most pesticides; however, there is a considerable 

amount of field data related to poisoning of nontarget wildlife with anticoagulant rodenticides. This 
33

information provides a weight-of-evidence approach to conservatively evaluate the risk of 

brodifacoum to nontarget organisms. The conservative assumptions regarding the potential for 

exposure to human health, nontarget species, and the environment address the uncertainties to 

some extent. A lack of risk using these conservative assumptions supports the reasonable 

certainty that impacts on human health and the environment will be negligible. However, primary,

and secondary risks to nontarget mammals are not negligible, particularly for broadcast 

applications.

Another area of potential uncertainty in this risk assessment is the potential for cumulative impacts 

on human health, nontarget species, and the environment from the proposed use of brodifacoum

by WS. Areas where cumulative impacts could occur are: 1) repeated worker and environmental 

exposures to brodifacoum from program application; 2) co-exposure to other chemicals with a 

similar mode of action; and 3) exposures to other chemicals affecting the toxicity of brodifacoum.

Repeated exposures that increase risk of injury from accidental brodifacoum exposure by WS 

applications are expected to be minimal due to strict WS applicator adherence to label-required 

PPE. Additionally, the labels limit the application frequency, the maximum amount allowed during 

each application, and the total amount allowed overall.

7 PREPARERS: WRITERS, EDITORS, AND REVIEWERS 

7.1 APHIS WS Methods Risk Assessment Committee

Writers for “Use of Brodifacoum in Wildlife Damage Management Risk Assessment”:

Writer: Jim Warren 

Position: USDA-APHIS-Policy and Program Development (PPD), Environmental and Risk 

Analysis Services (ERAS), Environmental Toxicologist, Little Rock, AR 

Education: B.S. Forest Ecology and M.S. Entomology – University of Missouri; Ph.D. 

Environmental Toxicology – Clemson University

Experience: Eighteen years of experience working for APHIS preparing ecological risk 

assessments and providing environmental compliance support. Prior experience before 

joining APHIS includes other government and private sector work regarding ecological risk 

assessments related to various environmental regulations.

Writer: Andrea Lemay 

Position: USDA-APHIS-Policy and Program Development (PPD), Environmental and Risk 

Analysis Services (ERAS), Biological Scientist, Raleigh, NC

Education: BS Plant and Soil Science (Biotechnology) - University of Massachusetts; MS Plant 

Pathology - North Carolina State University 

Experience: Thirteen years of service in APHIS conducting risk analysis. Nine years of 

experience in preparing environmental analyses in compliance with the National 

Environmental Policy Act.

Editors/Contributors for “Use of Brodifacoum in Wildlife Damage Management Risk 

Assessment”:

Editor: Shelagh DeLiberto 
34

Position: USDA-APHIS-Wildlife Services (WS), National Wildlife Research Center (NWRC), 

Wildlife Biologist, Fort Collins, CO

Education: BA Biology and Environmental Science – Ithaca College; MS Wildlife Biology –

Colorado State University 

Experience: Twenty years of service in APHIS conducting wildlife research. Four years of 

experience preparing categorical exclusions and environmental analyses in compliance with 

the National Environmental Policy Act.

Editor: Emily Ruell

Position: USDA-APHIS-WS, NWRC, Registration Manager, Fort Collins, CO

Education: B.S. Zoology and Biological Aspects of Conservation – University of Wisconsin -

Madison; M.S. Ecology – Colorado State University (CSU); M.A. Political Science – CSU

Experience: Nine years of experience with APHIS WS NWRC preparing and reviewing 

vertebrate pesticide registration data submissions and other registration materials, and 

providing pesticide regulatory guidance to WS, WS NWRC, and collaborators. Prior 

experience before joining APHIS includes seven years of conducting field and laboratory 

wildlife research at CSU, and environmental policy research for the U.S. Geological Survey.

Contributor: Thomas C. Hall

Position: USDA-APHIS-WS, Operational Support Staff, Staff Wildlife Biologist, Fort Collins, CO

Education: BS Biology (Natural History) and BA Psychology – Fort Lewis College; MS Wildlife 

Ecology – Oklahoma State University

Experience: Special expertise in wildlife biology, identification, ecology, and damage 

management. Thirty-seven years of service in APHIS Wildlife Services including operations 

and research in CO for research and OR, GU, CA, OK, and NV for operations conducting a 

wide variety of programs including bird damage research and management, livestock 

protection, invasive species management, wildlife hazard management at airports, property 

and natural resource protection including waterfowl, brown tree snake, feral swine, rodent, 

and beaver damage management. Applied and supervised chlorophacinone use.

7.2 Internal Reviewers

USDA APHIS Wildlife Services

Reviewer: Sarah K. Hibbs-Shipp, PhD

Position: Regulatory Support Services Unit Leader (Technology Transfer Manager)

Education: BA Biology – Grinnell College, Grinnell, IA; MS & PhD Nutrition Science – Colorado 

State University, Fort Collins, CO.

Experience: One year of regulatory review experience with the National Wildlife Research 

Center, providing guidance and editorial review for pesticide and other briefing content. Prior 

to joining the USDA, five years of technology transfer/product development work with 

Colorado State University, which included developing/authoring and reviewing lay public 

oriented science communication briefs and non-confidential technology summaries. 

Previous to CSU, thirteen years of clinical research and development study management for 

Phase I-IV dermatology-focused and other non-life-threatening drug development regulated 

research submitted to the FDA, as well as extensive safety, efficacy, and claim 

substantiation research for inclusion in FTC review packages prior to marketing 

implementation.

Reviewer: Rickey L. Gilliland
35

Position: District Supervisor Wildlife Biologist USDA-APHIS-WS 

Education: BS Oklahoma State University – Wildlife Ecology

Experience: 34 years of field and supervisory experience which includes field rodent control 

and disease research (Texas Wildlife Services Program)
36

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